refactor: use robots and sitemap metadata

app/robots.ts

@@ -0,0 +1,13 @@
+import { MetadataRoute } from 'next'
+import siteMetadata from '@/data/siteMetadata'
+
+export default function robots(): MetadataRoute.Robots {
+  return {
+    rules: {
+      userAgent: '*',
+      allow: '/',
+    },
+    sitemap: `${siteMetadata.siteUrl}/sitemap.xml`,
+    host: siteMetadata.siteUrl,
+  }
+}